A pilot study evaluating 2D antiscatter grid based scatter suppression for quantitative cone beam CT in radiotherapy

Area of Science:

• Medical Imaging Physics
• Radiotherapy Technology
• Diagnostic Radiology

Background:

• Cone beam CT (CBCT) images often exhibit poor CT number accuracy due to X-ray scatter.
• Inaccurate CBCT data hinders online dose calculations, structure segmentation, and response assessment in radiotherapy.
• A novel 2D antiscatter grid was developed to mitigate scatter and improve CBCT fidelity, termed quantitative CBCT (qCBCT).

Purpose of the Study:

• To evaluate the impact of a novel 2D antiscatter grid on CBCT image quality and quantitative accuracy.
• To compare the performance of quantitative CBCT (qCBCT) against standard clinical CBCT protocols.
• To assess the effectiveness of qCBCT in reducing CT number errors and artifacts.

Main Methods:

• A prospective trial involving 31 patients undergoing radiotherapy.
• CBCT scans were acquired using both standard clinical protocols and the qCBCT system with a 2D antiscatter grid.
• CT number errors, artifact amplitudes, and contrast-to-noise ratio (CNR) were quantitatively compared between standard CBCT and qCBCT.

Main Results:

• qCBCT reduced absolute CT number errors by up to 56% and artifact amplitudes by up to 53% compared to clinical CBCT.
• CNR was 20% higher in iterative reconstruction clinical CBCT but 11% lower in standard clinical CBCT relative to qCBCT.
• Significant improvements in CT number accuracy and artifact reduction were observed in patients with larger lateral separations and in the lower neck region.

Conclusions:

• Hardware-based scatter mitigation using a 2D antiscatter grid significantly enhances CT number accuracy in CBCT.
• qCBCT offers improved quantitative accuracy compared to existing clinical CBCT methods.
• The benefits of qCBCT are particularly notable in challenging anatomical regions and for patients requiring precise dose calculations.